The present invention relates to a metal gasket sandwiched between two members for sealing therebetween, and more specifically, a metal gasket being able to obtain an substantially equal sealing surface pressure all around a sealing bore while controlling a deformation of members sandwiching the metal gasket such as a deformation of a cylinder bore, flange or the like.
Cylinder head gaskets or gaskets for intake and exhaust manifolds are used in a state of being sandwiched between a cylinder head and a cylinder block (cylinder body) of an automobile engine, or between the intake manifold and the intake pipe and between the exhaust manifold and the exhaust pipe; and are tightened by fastening bolts to seal fluid such as combustion gas, oil, coolant water and the like.
Due to a recent lightweight and downsized engine, the engine has a low rigidity, and engine members have also low rigidities. As a result, a deformation can occur in the sealing bore such as the cylinder bore, flange or the like, or the periphery portion thereof. If the cylinder bore, flange or the like is deformed, a sealing means such as beads or the like does not function completely, so that adequate sealing performance cannot be obtained.
As one of countermeasures with respect to the above-mentioned problem, the following metal laminate gasket is proposed. A first bead is provided inside a folded portion, and a second bead is provided on the outer-periphery side of the first bead. The folding width of the folded portion away from a tightening bolt is formed narrower than that of neighboring portion of the tightening bolt. In addition, the bead width of one of the first bead or the second bead, or both the first bead and the second bead, is formed narrower at a portion away from the tightening bolt than the neighboring portion of the tightening bolt (for example, refer to Japanese Patent Publication (TOKKAI) No. H11-118037).
The metal laminate gasket with the above-mentioned structure equalizes the tightening load, prevents the deformation of a bore, and has an excellent gas sealing performance. However, the first bead and the second bead are provided on a sealing bore side rather than the neighboring portion of the bolt hole, and also width of an inside folded portion and the first bead or the second bead is all formed wide at the portion away from the tightening bolt in the same way. As a result, depending on the shape of a sealing member or the type of a gasket, the second bead, which has wide neighboring portion of the bolt hole and a relatively small compression resistance, might receive a fastening force applied to the neighboring portion of the bolt hole, thereby becoming flattened. Consequently, the first bead also might be flattened.
An object of the present invention is to provide a metal gasket which can obtain an approximately equal sealing surface pressure all around the sealing bore by combining inner-periphery side bead and outer-periphery side bead whose compression resistances change in the periphery direction; provide excellent sealing abilities; and control a flexural deformation of the cylinder head or the flanges of the intake and exhaust manifolds which are joint surfaces.
Further objects and advantages of the invention will be apparent from the following description of the invention.